Computer controlled printer techniques are wide-spread in business and industrial applications. Laser type printers are rapidly replacing impact-type printers of the wire-dot and daisy wheel type, as well as ink jet and thermal printers. Additionally, many processes that were entirely manual are being replaced by computers and computer displays. For example, during the past decade, computer aided design (CAD) and computer aided engineering (CAE) markets have demonstrated remarkable growth. Ultimately, the work product that is initially presented on a visual display, such as a cathode ray tube or a liquid crystal screen, must be reduced to a hard copy, that is, a paper or film copy.
In all such scanning and electronic and printing applications, image reproduction quality is extremely important, but especially so with CAD/CAE, where extremely wide outputs, as much as 36 inches wide, are required for paper and photographic copies.
To use current technology to provide wider outputs, unit pricing becomes very high and restricts usage of wide output devices to larger users. Also, wider format devices operate at limited production speeds, thus reducing productivity for the user. For these reasons, wide format output devices are typically not used for proofing applications in printing and publishing, where the need or such wide formats is growing.
With regard to CAD/CAE, pen plotters and electrostatic printers have until recently filled the need for hard copies. Such printers/plotters are generally low cost and very reliable. However, they have a slow operating speed and fairly high maintenance requirements to keep the pen and ink elements from clogging or being contaminated by paper fibers.
Wide format thermal plotters are available, but are limited to a maximum resolution of 400 dots per inch (dpi) due to the difficulty of laying down uniform controllable heating elements of such small dimension. Further, thermal devices require the use of specially coated imaging materials at a considerable ongoing expense to users of these devices.
Laser systems have become the technology of choice over previously discussed technologies. Generally, mechanical means are required to transmit information coded laser light in a linear format to a photosensitive record carrier. Such mechanical devices frequently include a rotating mirror system and optical elements. As wider printing formats are required, the optical and mechanical complexities increase, reliability decreases, and wider format laser printers become very costly and, therefore, less desirable.
Cathode ray tubes (CRT) have also been used as a source of optically presented data that is transmitted to the photosensitive device by way of optical elements. For transmitting this data to the photosensitive medium, systems have been developed using coherent fiber arrays, as well as arrays of fibers that are linear at one end and random at the other end. U.S. Pat. No. 4,674,834 indicates how the face of a cathode ray tube is used as a light input to a randomly arranged array of optical fibers. The other ends of the fiber array are arranged linearly opposing a printing drum so the light is received on a line-by-line basis. Synchronized computer circuitry is required to linearize (electronically) the randomly arrayed optical signals based on stored information as to which fibers at the random end correspond to the successive linear fibers at the other end. Thus, there is a two-step process requiring calibration and data storage to deliver light signals in proper sequence to the printing mechanism.
High resolution imaging with fiber arrays has not been practical due to the difficulty in handling small diameter optical fibers, and matching them to the cathode ray tube. Any fiber defect can cause a streak in the image, and thus, make the array unusable. The image spot on the cathode ray tube face has been limited by the size and shape of the individual fibers and the cathode ray tube spot size must be smaller than the individual fiber to ensure proper imaging and minimize the effects of drift on the cathode ray tube screen.
What are needed are optical scanners and printers capable of scanning and printing, respectively, large widths for photographic and plain paper applications with high resolution, reliability, a minimal number of moving parts in the optical system, and low cost. This invention addresses solutions to all of the above requirements.